This section provides background information related to the present disclosure which is not necessarily prior art.
A recloser is a type of a breaking device which is configured so as to, if a failure occurs in an overhead line, automatically detect the same and break a power supplied thereto through opening the line, and if the failure is overcome, supply the power through automatically connecting the line, and is a device which is installed on the overhead line to protect a transformer upon the occurrence of an over load or abnormal state, and prevent the extent of electrical failure from being enlarged. When classifying the recloser depending on an operating mechanism, it may be divided into a type using a spring and a rotary motor, and a type using a permanent magnet operating device (hereinafter, also referred to as a permanent magnet actuator, PMA). The recloser using the permanent magnet actuator may be manufactured in a simpler structure, and used in a higher frequency of use due to a high reliability in operation than the type using the spring. The permanent magnet actuator may be manufactured in a small size but generate a large force, and in particular, has characteristics of being capable of generating a very large force at each end of a stroke, which is ideally suited to the requirement of a greater holding force when the line is opened or connected in the recloser.
The permanent magnet actuator is an actuator which is configured so that a movable element reciprocates by a coercive force of a permanent magnet and a magnetomotive force derived from a coil. There are one-coil type and two-coil type permanent magnet actuators, and the two-coil type permanent magnet actuator is more frequently applied for use as a recloser.
A structure of a general permanent magnet actuator is already well known in the art through Korean Patent Laid-Open Publication No. 10-2004-0035176, Korean Utility Model Registration Publication No. 20-0401042, and the like.
FIG. 1 is a view illustrating an operation principle of a conventional two-coil type permanent magnet actuator in the related art, and FIG. 2 is a view illustrating an example of a driving circuit for driving the permanent magnet actuator of FIG. 1.
The conventional permanent magnet actuator includes a stator iron core 10, a movable element 20, a permanent magnet 30, a first coil 40 and a second coil 50. The stator iron core 10 is formed by laminating a plurality of iron plates which are magnetic materials, and has a first wall 11 and a second wall 13 which faces the first wall to define a space 15 therein. The movable element 20 is positioned in the space 15 to reciprocate between the first wall 11 and the second wall 13 along an imaginary moving axis connecting the first wall 11 and the second wall 13. In addition, the movable element 20 may include a driving shaft 21 which is disposed in a structure of penetrating the first wall 11 and the second wall 13 to guide a reciprocation thereof. Further, when being used in an apparatus such as the recloser, the above-described driving shaft 21 plays a role of an element for connecting the permanent magnet actuator with another mechanical element. The first coil 40 and the second coil 50 serve to provide the magnetomotive force to the movable element 20 for reciprocating the same. Herein, the first coil 40 is located on the first wall 11 side, and the second coil 50 is located on the second wall 13 side in the space 15. The permanent magnet 30 is disposed between the first coil 40 and the second coil 50 to provide the coercive force to the movable element 20. The first coil 40 and the second coil 50 are wound in a direction orthogonal to a direction in which the movable element 20 moves, respectively, and thus to generate magnetomotive forces in different directions from each other.
FIG. 1a illustrates a state that the movable element 20 is positioned on the first wall 11 side in which the first coil 40 is located in the space 15 inside the stator iron core 10. In this case, the movable element is maintained with being attached to the first wall 11 due to a coercive force M1 provided by the permanent magnet 30. In this state, as illustrated in FIG. 1b, when a current is supplied to the second coil 50 by closing a switching device 51 connected to the second coil 50 by a control unit 60, a second wall-direction magnetomotive force E2 is generated in the second coil 50, and when a second wall-direction force which is larger than a force that pulls the movable element 20 by the coercive force M1 of the permanent magnet 30 is generated by the second wall-direction magnetomotive force E2, the movable element 20 moves to the second wall 13 side in which the second coil 50 is located. As a result, the movable element 20 is maintained with being attached to the second wall 13. In this state, even when the current is not supplied to the second coil 50 by opening the switching device 51 connected to the second coil 50, the movable element 20 is maintained with being attached to the second wall 13 by a coercive force M2 provided by the permanent magnet 30, as illustrated in FIG. 1c. In this state, when the current is supplied to the first coil 40 by closing a switching device 41 connected to the first coil 40 by the control unit 60, a first wall-direction magnetomotive force E1 is generated in the first coil 40, and as illustrated in FIG. 1d, when a first wall-direction force which is larger than a force that pulls the movable element 20 by the coercive force M2 of the permanent magnet 30 is generated by first wall-direction magnetomotive force E1, the movable element 20 moves to the first wall 11 side in which the first coil 40 is located. In this state, even when the current is not supplied to the first coil 40 by opening the switching device 41 connected to the first coil 40, the movable element 20 is maintained with being attached to the first wall 11 by the coercive force M1 provided by the permanent magnet 30, as illustrated in FIG. 1a. 
In the operation principle of the permanent magnet actuator as described above, in order to move the movable element 20 stopped with being attached to the first wall 11 or the second wall 13 to an opposite wall side, it is necessary for the second coil 50 or the first coil 40 located at opposite sides to generate a force larger than the force that pulls the movable element 20 by the coercive force M1 or M2 of the permanent magnet 30. Therefore, a large amount of current should be supplied to the first or second coil to obtain the larger magnetomotive force E2 or E1. When applied for use in the recloser, the permanent magnet actuator should be supplied with the current through a capacitor. Therefore, supplying a large amount of current means that there is no choice but requiring a large capacitance of capacitor, and increasing a current capacity of the devices used in the driving circuit, as well as, this may be a factor to hinder a decrease in a size of the recloser, and to increase production costs.
FIG. 3 is a view illustrating another example of the conventional permanent magnet actuator in the related art, and FIG. 4 is another example of the conventional permanent magnet actuator in the related art.
The permanent magnet actuators illustrated in FIGS. 3 and 4 are adapted to reduce the supplied current, and may be configured so as to provide a large holding force at one end of a stroke (in order to maintain a pressure of circuit contacts), while provide a relative smaller holding force at the other end of the stroke. For example, as illustrated in FIG. 3, when including a groove 12 on the first wall 11 side capable of housing a portion of the movable element 20, a smaller holding force is applied to the movable element 20 with being located on the first wall 11 side in which the groove 12 is positioned, while a larger holding force is applied thereto with being located on the second wall 13 side. Herein, the groove 12 serves to prevent a rapid change in a permeance with respect to a displacement of the movable element 20 (the holding force is proportional to a variation in the permeance according to the displacement of the movable element). As another example, as illustrated in FIG. 4, when including a non-magnetic material 16 disposed between the first wall 11 and the movable element 20, a smaller holding force is applied to the movable element 20 with being located on the first wall 11 side in which the non-magnetic material 16 is positioned, while a larger holding force is applied thereto with being located on the second wall 13 side (also in this case, the variation in the permeance according to the displacement of the movable element 20 is decreased). As described above, when the holding force acting on the movable element 20 may be smaller, it is advantageous since the amount of current that should be supplied to the coil of the opposite side (the second coil in FIGS. 3 and 4) for moving the movable element to the opposite side can be reduced. However, also in the case of the permanent magnet actuators illustrated in FIGS. 3 and 4, when the movable element 20 is located on the second wall 13 side, the holding force is large (in order to maintain the pressure of the circuit contacts, it is not possible to decrease the holding force). Therefore, in order to move the movable element to the first wall 11 side, it is still necessary to supply a large amount of current to the first coil 40.